How to generate an horizontal color axis in pyx density style?

Question

In python pyx one can make color density plots such as this example:

from pyx import *

# Mandelbrot calculation contributed by Stephen Phillips

# Mandelbrot parameters
re_min = -2
re_max = 0.5
im_min = -1.25
im_max = 1.25
gridx = 100
gridy = 100
max_iter = 10

# Set-up
re_step = (re_max - re_min) / gridx
im_step = (im_max - im_min) / gridy
d = []

# Compute fractal
for re_index in range(gridx):
    re = re_min + re_step * (re_index + 0.5)
    for im_index in range(gridy):
        im = im_min + im_step * (im_index + 0.5)
        c = complex(re, im)
        n = 0
        z = complex(0, 0)
        while n < max_iter and abs(z) < 2:
            z = (z * z) + c
            n += 1
        d.append([re, im, n])

# Plot graph
g = graph.graphxy(height=8, width=8,
                  x=graph.axis.linear(min=re_min, max=re_max, title=r"$\Re(c)$"),
                  y=graph.axis.linear(min=im_min, max=im_max, title=r'$\Im(c)$'))
g.plot(graph.data.points(d, x=1, y=2, color=3, title="iterations"),
       [graph.style.density(gradient=color.rgbgradient.Rainbow)])

g.writePDFfile()

The problem with that color legend is that if I have a page with fixed width, the whole image gets rescaled such that the width of the graph is reduced with respect to other graphs, in order to include the color bar. I would like to make the color bar horizontal above the graph to avoid this problem. Is there any easy fix to this? I could not find anything on the manual.

Answer 1

You can generate the keygraph yourself with settings as needed:

kg = graph.graphx(ypos=-3, length=8, direction="horizontal", x_title="iterations")

and pass it to the density style:

g.plot(graph.data.points(d, x=1, y=2, color=3),
       [graph.style.density(gradient=color.rgbgradient.Rainbow, keygraph=kg)])

In order to see it, also need to add it to the graph (which is a canvas) like this:

g.insert(kg)

Result: